feat(evmigration): tune migration params, fix chain-helper counts

[akobrin1]

Summary

Finalizes the x/evmigration launch parameters and hardens the supporting chain-helper.sh tooling, plus syncs the rollout doc.

• max_validator_delegations default 2000 → 2500 (x/evmigration/types/params.go). Sized against live lumera-mainnet-1, where the largest validator's migration-object count (delegations + unbondings + redelegations) is 1,632; 2500 gives ~1.5× headroom without over-provisioning.
• Devnet migration_end_time auto-derived in the v1.20.0 upgrade handler as upgrade-block time + 2 days (app/upgrades/v1_20_0/upgrade.go). Testnet/mainnet keep 0 and receive a specific absolute Unix timestamp near launch.
• Chain-ID detection moved to config (IsDevnetChainID, etc.) as a single source of truth; app/upgrades/chain_id.go delegates to it — this avoids the import cycle that blocks v1_20_0 from importing package upgrades.
• EvmigrationKeeper wired into AppUpgradeParams so the handler can set params.
• scripts/chain-helper.sh fixes: max-validator-delegations now uses --page-count-total for exact counts (was silently truncated at the page limit, e.g. 1,593 → 1,000); added per-validator count= progress; default buffer 10% → 30%.
• New stats command: total accounts, validators + jailed count, supernodes grouped by current state.
• Docs: rollout.md updated with the finalized decisions (also synced to the Notion page).
• CI setup cleanup: the shared setup-go action now owns Go dependency caching/downloads, so the build/test workflows no longer repeat explicit go mod download steps.

Test plan

• go build ./... — clean
• go test ./config/... ./app/upgrades/... ./x/evmigration/... — all pass (incl. new devnet migration_end_time upgrade tests)
• golangci-lint run on changed packages — 0 issues
• bats tests/scripts/chain-helper.bats — 8/8 pass
• chain-helper.sh stats / max-validator-delegations verified live against lumera-mainnet-1

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR finalizes x/evmigration launch sizing and makes the v1.20.0 upgrade path/network tooling more robust by (a) auto-deriving devnet/testnet migration deadlines at upgrade time, (b) consolidating chain-ID classification, and (c) hardening chain-helper.sh counting + adding a new stats command. It also updates rollout documentation and refactors GitHub Actions Go setup to prime module caches centrally.

Changes:

• Tune x/evmigration defaults (notably max_validator_delegations → 2500) and document sizing rationale.
• In the v1.20.0 upgrade handler, auto-set migration_end_time on devnet/testnet from upgrade block time; mainnet remains 0.
• Improve operational tooling (chain-helper.sh exact counting + new stats) and supporting tests/docs; CI workflows now rely on a smarter setup-go composite action.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
x/evmigration/types/params.go	Raises DefaultMaxValidatorDelegations to 2500 and documents sizing rationale.
tests/scripts/chain-helper.bats	Updates Bats fixtures/assertions for exact pagination totals and the new stats command.
scripts/chain-helper.sh	Fixes staking record counting via --page-count-total, adds progress detail, and introduces stats with pagination helper.
docs/evm-integration/architecture/rollout.md	Updates rollout decisions/table to reflect finalized migration policy and sizing signals.
devnet/tests/common/chaincli.go	Improves height parsing to handle mixed CLI output and top-level header.height.
devnet/tests/common/chaincli_test.go	Adds coverage for the new LatestHeight parsing cases.
config/config.go	Centralizes chain-ID prefix constants and Is{Net}ChainID helpers.
app/upgrades/v1_20_0/upgrade.go	Adds auto-derived migration window logic and sets migration_end_time on devnet/testnet.
app/upgrades/v1_20_0/upgrade_test.go	Adds tests asserting devnet/testnet deadline derivation and mainnet “leave at 0”.
app/upgrades/params/params.go	Wires EvmigrationKeeper into AppUpgradeParams.
app/upgrades/chain_id.go	Delegates chain-ID checks to config to avoid import cycles.
app/app.go	Passes EvmigrationKeeper into upgrade params wiring.
.github/workflows/test.yml	Removes redundant go mod download steps (now handled by composite action).
.github/workflows/build.yml	Same CI adjustment as above across build/test jobs.
.github/actions/setup-go/action.yml	Enhances Go setup to optionally download modules and explicitly cache GOMODCACHE.

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